The California Department of Food and Agriculture (CDFA) reported Feb. 21 that a case of equine herpesvirus myeloencephalopathy (EHM), the neurologic form of equine herpesvirus-1 (EHV-1), has been confirmed at Los Alamitos Race Course, in Cypress, California.

“A 10-year-old pony horse at Los Alamitos Race Course displaying severe neurologic signs was euthanized and confirmed positive the wild-type strain of equine herpesvirus-1,” the CDFA said on its website. “A quarantine has been issued for exposed horses. CDFA and California Horse Racing Board staff are onsite ensuring biosecurity measures are implemented.”

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and EHM (the neurologic form). In many horses, the only sign of EHV-1 infection is fever, which can go undetected.

In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months), but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1